Run-flat tire

ABSTRACT

A run-flat tire is provided in which the tire uniformity is improved, as well as the durability during run-flat traveling may be improved drastically without deteriorating the ride quality during normal traveling. The run-flat tire comprises a side reinforcing rubber layer having a crescent-shaped meridional cross section which layer extends all over or almost all over the both side portions along the inside of the carcass ply. The carcass ply cord contains at least 50% by mass of polyketone fibers, has a heat shrinkage force of 0.1 to 1.8 cN/dtex as a cord subjected to a dipping process, and the heat shrinkage rate of the polyketone fiber in a dry heat treatment at a temperature of 150° C. for 30 minutes is in a range of 0.3 to 6.5%; and the carcass ply includes a weft which crosses the cords arranged approximately along the radial directions, and the weft is cut at a plurality of points at regular intervals along the tire circumferential direction.

TECHNICAL FIELD

The present invention relates to a run-flat tire, particularly to a side reinforcing type run-flat tire in which the durability during run-flat traveling is improved drastically without deteriorating the ride quality during normal traveling.

BACKGROUND ART

As a so-called run-flat tire with which a vehicle can travel some amount of distance in safety without losing the tire's load-supporting ability even in the state that the inner pressure of the tire is decreased due to a puncture or the like, a variety of side reinforcing type run-flat tires such as a tire in which a side reinforcing rubber layer having a relatively high modulus and having a crescent-shaped cross-section is located inside the carcass in the side wall portion of the tire to increase the rigidity of the side wall portion thereby enabling the tire to bear a load without extremely increasing the deformation of the side wall portion of the tire at the time when the inner pressure is decreased, a tire the side wall portion of which is reinforced with a variety of reinforcing members, and the like have been proposed (See Patent Documents 1 to 4).

On the other hand, because cellulosic fibers such as rayon have a high modulus at room temperature and a high adhesiveness to rubber, they have been used as a reinforcement for a variety of rubber goods including a reinforcing cord for tires. In addition, the cellulosic fiber has a higher Young's modulus at room temperature and at a high temperature than polyesters such as polyethylene terephthalate (PET), and has a high thermal dimensional stability such that the heat shrinkage at a temperature of 177° C. is 0.65 to 1.0%. Therefore, the cellulosic fiber has also been used for a reinforcing cord for the carcass of the above-described side reinforcing type run-flat tire.

However, as for a conventional side reinforcing type run-flat tire using a cellulosic fiber cord such as rayon as a reinforcing cord for the carcass, the deformation of the tire during run-flat traveling is large because the modulus of elasticity of the cellulosic fiber is not sufficiently high, and the deformation of the tire is still larger when the temperature of the tire becomes high due to run-flat traveling because the rigidity of a carcass ply decreases. Thus, the main cause of failure of the tire at the end phase of run-flat travel is a fracture in the side reinforcing rubber layer having the above-described crescent-shaped cross-section, and there has been a problem for conventional side reinforcing type run-flat tires in that the durable distance of the run-flat traveling is short.

On the other hand, there is a problem that ride quality during normal traveling deteriorates when the side wall portion is reinforced, for example, by thickening the gauge of the side reinforcing rubber layer in order for the tire to prolong the durable distance during run-flat traveling because the weight of the tire increases or a vertical stiffness of the tire during normal traveling increases.

In order to overcome such a problem, the present inventors have previously reported in Patent Document 5 that the deformation of the tire during run-flat traveling may be controlled without increasing the weight of the tire by employing a polyketone fiber cord having a specific heat shrinkage force and modulus of elasticity as a reinforcing cord of the carcass of the side reinforcing type run-flat tire, therefore a run-flat durability of the tire may be improved drastically without deteriorating the ride quality during normal traveling.

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-264012 Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-500587 Patent Document 3: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-500589 Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-306658 Patent Document 5: Japanese Unexamined Patent Application Publication No. 2006-224952 DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

As for the run-flat tire described in Patent Document 5, the run-flat durability of the tire may have been improved drastically without deteriorating the ride quality during normal traveling, though, the side reinforcing type run-flat tire has had a problem that the uniformity of the tire deteriorates more than that of a conventional tire because the vertical stiffness of the side reinforcing type run-flat tire during normal traveling is large.

Therefore, an object of the present invention is to overcome the problem of the above-described conventional art, thereby providing a run-flat tire in which the tire uniformity is improved, as well as the durability during run-flat traveling may be improved drastically without deteriorating the ride quality during normal traveling.

Means for Solving the Problem

To attain the above-described object, the present inventors intensively studied to discover that the deformation of the tire during run-flat traveling may be controlled without increasing the weight of the tire by employing organic fiber cords mainly including a polyketone fiber having physical properties such as a specific heat shrinkage force and the like as a reinforcing cord of the carcass of the side reinforcing type run-flat tire and, in addition, cutting the weft which crosses the reinforcing cord of the carcass at a plurality of points along the tire circumferential direction at a specified cutting pitch, therefore while a run-flat durability of the tire may be improved drastically without deteriorating the ride quality during normal traveling, homogeneity along the tire circumferential direction may be improved and deterioration of uniformity may be controlled, thereby completing the present invention.

That is, the run-flat tire of the present invention is a run-flat tire comprising a left-and-right pair of bead portions, a carcass ply extending from a crown portion to the pair of bead portions by way of each of the side portions, and a side reinforcing rubber layer having a crescent-shaped meridional cross section which layer extends all over or almost all over the both side portions along the inside of the carcass ply, wherein

the carcass ply cord contains at least 50% by mass of polyketone fibers, has a heat shrinkage stress of 0.1 to 1.8 cN/dtex as a dip treated cord, and the heat shrinkage rate of the polyketone fiber in a dry heat treatment at a temperature of 150° C. for 30 minutes is in a range of 0.3 to 6.5%; wherein

the carcass ply comprises a weft which crosses the cords arranged approximately along the radial directions, and the weft is cut at a plurality of points at regular intervals along the tire circumferential direction.

In the run-flat tire of the present invention, the end count of the polyketone fiber cords at the bead portion of the carcass ply is preferably in a range of 70 to 120 cords/100 mm, and the end count of the weft is preferably in a range of 3 to 20 cords/100 mm. Further, the cord diameter of D1 of the carcass ply cord is preferably in a range of 0.45 to 0.95 mm, and the diameter D2 of the weft is preferably in a range of 0.1 to 0.3 mm. Still further, as a polyketone fiber included in the fiber cord which forms the carcass ply, the tensile strength of the original yarn is preferably not less than 10 cN/dtex and the modulus of elasticity of the yarn is preferably not less than 60 cN/dtex, as well as the breaking elongation of the weft is preferably 5 to 20% and the breaking strength of the weft is preferably in a range of 200 to 1000 g. Still further, the weft is preferably composed of cellulosic fibers or vinylon fibers, and the weft is preferably spun yarn.

As used herein, the “heat shrinkage force” of the cord refers to the maximum force (unit: cN/dtex) generated in the cord at a temperature of 177° C., in which cord a 25 cm of fixed length sample of the carcass ply cord before vulcanization subjected to a general dipping process is heated at a rate of temperature rise of 5° C./min. The heat shrinkage rate of the polyketone fiber in a dry heat treatment is a value obtained by measuring the lengths of the fiber while applying a 1/30 (cN/dtex) of load before and after a heat treatment which is a dry heat treatment in an oven at a temperature of 150° C. for 30 minutes and applying the measured values to the following equation:

Heat Shrinkage Rate (%) in a dry heat treatment={(Lb−La)/Lb}×100,

where Lb is the length of the fiber before the heat treatment, and La is the length of the fiber after the heat treatment. The tensile strength and the tensile modulus of elasticity of the polyketone fiber are the values obtained by performing measurements in accordance with JIS-L-1013, and the tensile modulus of elasticity of the polyketone fiber is a value of the initial modulus of elasticity calculated by a load at an elongation of 0.1% and a load at an elongation of 0.2%.

EFFECTS OF THE INVENTION

The present invention may provide a run-flat tire in which the tire uniformity is improved, as well as the durability during run-flat traveling may be improved drastically without deteriorating the ride quality during normal traveling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-section of the right half of one example of the pneumatic tire of the present invention.

FIG. 2 illustrates a cross-section of a portion of a carcass ply in which portion carcass cords and wefts which cross the carcass cords are included.

REFERENCE NUMERALS

-   1 bead portion -   2 side wall portion -   3 tread portion -   4 radial carcass -   5 side reinforcing rubber layer -   6 bead core -   7 bead filler -   8 belt -   9A, 9B belt reinforcing layer -   10 carcass ply cord -   11 weft -   A cut pitch of weft

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the present invention will be described in detail referring to the drawings. FIG. 1 is a partial cross section of one example of the run-flat tire of the present invention. The tire shown in FIG. 1 has a left-and-right pair of bead portions 1, a pair of side wall portions 2 and a tread portion 3 connecting to both the side wall portions 2, and extends toroidally between the pair of bead portions 1, as well as the tire comprises a radial carcass 4 composed of one or more carcass plies which reinforce each of portions 1, 2 and 3, and comprises a pair of side reinforcing rubber layers 5 having a crescent-shaped cross section arranged inside of the radial carcass 4 in the side wall portions 2.

In the example of the tire illustrated in the drawing, a bead filler 7 is placed at the outside, in the tire radial direction, of a ring-shaped bead core 6 each embedded in the bead portion 1. In addition to that a belt 8 composed of two sheets of belt layers is placed at the outside, in the tire radial direction, of the crown portion of the radial carcass 4, a belt reinforcing layer 9A is placed such that the layer covers the whole of the belt 8 at the outside, in the tire radial direction, of the belt 8. Further, a pair of belt reinforcing layers 9B are placed such that the layers cover only both ends of the belt reinforcing layer 9A. In this case, the belt layer is normally composed of a rubberized layer comprising cords, preferably a rubberized layer comprising steel cords, the cords extending in a direction having an inclination relative to the tire equatorial plane. The two belt layers are piled such that the cords which constitute the belt layers cross each other across the equatorial plane to constitute the belt 8. The belt reinforcing layers 9A and 9B are usually composed of a rubberized layer comprising cords arranged substantially parallel to the tire circumferential direction.

The radial carcass 4 in the example illustrated in the drawing is constituted by one sheet of carcass ply which is a plurality of reinforcing cords arranged parallel to each other covered with a coating rubber, and the radial carcass 4 is composed of a main body which extends toroidally between a pair of bead cores 6 embedded in each of the above-described bead portions 1, and a pair of turn-up portions where the carcass curls up around each of bead cores 6 from the inside to the outside of the tire width direction and outward in the radial direction. The number of plies and structure of the radial carcass 4 in the pneumatic tire of the present invention are not limited thereto. The belt 8 in the example illustrated in the drawing is composed of two sheets of the belt layers, though in the pneumatic tire of the present invention the number of sheets of the belt layers which constitute the belt 8 is not limited thereto. In the pneumatic tire of the present invention, the belt reinforcing layers 9A and 9B are not necessarily installed, and a belt reinforcing layer having another structure may also be installed.

In the present invention, it is preferred that at least 50%, preferably 70%, and more preferably 100% by mass of polyketone fibers is included in a carcass ply cord of the radial carcass 4. When polyketone fiber included in the carcass ply cord is less than 50% by mass, any one of the performances that are the strength of the tire, the heat resistance of the tire and the adhesiveness with the rubber are insufficient.

Further, it is preferred that a carcass ply cord of the radial carcass 4 has a heat shrinkage stress in a range of 0.1 to 1.8 cN/dtex, more preferably 0.4 to 1.6 cN/dtex, still more preferably 0.6 to 1.4 cN/dtex. When the heat shrinkage force of the carcass ply cord is less than 0.1 cN/dtex, run-flat traveling durability may not be improved enough. On the other hand, when the heat shrinkage force of the carcass ply cord is more than 1.8 cN/dtex, it is feared that the shape of the finished tire deteriorates because the cord shrinks significantly due to the application of heat during the production of the tire.

Further, it is preferred that polyketone fiber included in the carcass ply cord of the radial carcass 4 has a heat shrinkage rate in a range of 0.3 to 6.5%, preferably 0.3 to 3% in a dry heat treatment at a temperature of 150° C. for 30 minutes. When the heat shrinkage rate in the dry heat treatment at a temperature of 150° C. for 30 minutes is less than 0.3%, the paralleling efficiency due to the application of heat during the production of the tire decreases significantly, resulting in insufficient strength of the tire. On the other hand, when the heat shrinkage rate in the dry heat treatment at a temperature of 150° C. for 30 minutes is more than 6.5%, it is feared that the shape of the finished tire deteriorates because the cord shrinks significantly due to the application of heat during the production of the tire.

Still further, as shown in FIG. 2, the carcass ply includes a weft 11 which crosses carcass ply cord 10 arranged approximately in the radial direction, and the weft is cut at a plurality of points at regular intervals along the tire circumferential direction. The weft 11 preferably has an end count in a range of 3 to 20 cords/100 mm. When the end count is less than 3 cords/100 mm, deterioration of the properties of a woven screen fabric is caused, thus the homogeneity in the tire circumferential direction may not be sufficiently improved. On the other hand, it is not preferred that the end count is more than 20 cords/100 mm because the weft 11 is hard to cut. As a means of cutting the weft 11, a conventional method described in, for example, Japanese Unexamined Patent Application Publication No. H05-208458 may be employed, and naturally, the other methods may also be employed to cut the weft.

Still further, the bead portion of the carcass ply preferably has an end count of the carcass ply cord in a range of 70 to 120 cords/100 mm, more preferably in a range of 85 to 110 cords/100 mm. When the end count is less than 70 cords/100 mm, the homogeneity in the tire circumferential direction may not be sufficiently improved. On the other hand, it is feared that the carcass cord may suffer damage during a weft cutting process when the end count is more than 120 cords/100 mm.

Still further, the cord diameter D1 of the carcass ply cord of the radial carcass 4 is preferably in a range of 0.45 to 0.95 mm. When the cord diameter D1 is less than 0.45 mm, it is feared that the carcass cord may suffer damage during the weft cutting process. On the other hand, when the cord diameter D1 is more than 0.95 mm, deterioration of the properties of a woven screen fabric is caused, thus the homogeneity in the tire circumferential direction may not be sufficiently improved.

Still further, the diameter D2 of the weft 11 is preferably in a range of 0.1 to 0.3 mm. When the diameter D2 is less than 0.1 mm, the weft 11 is cut unexpectedly before a process that a rubber is topped, thus the shape as a woven screen fabric may not be maintained. On the other hand, when the cord diameter D2 of the weft 11 is more than 0.3 mm, deterioration of the properties of a woven screen fabric is caused, thus the homogeneity in the tire circumferential direction may not be sufficiently improved.

Still further, as shown in FIG. 2, the cut pitch A of the weft 11 is preferably in a range of 5.5 to 60 times, more preferably in a range of 8 to 24 times the cord diameter D1. When the cut pitch A is less than 5.5 times the cord diameter D1, it is feared that the carcass cord may suffer damage during the cutting process. On the other hand, the cut pitch A is more than 60 times the cord diameter D1, the homogeneity in the tire circumferential direction may not be sufficiently improved.

Still further, polyketone fiber included in the carcass ply cord of the radial carcass 4 preferably has a tensile strength of not less than 10 cN/dtex, more preferably not less than 15 cN/dtex. When the tensile strength is less than 10 cN/dtex, the strength of the tire is insufficient.

Still further, polyketone fiber included in the carcass ply cord of the radial carcass 4 preferably has a modulus of elasticity of not less than 60 cN/dtex, more preferably not less than 80 cN/dtex. When the modulus of elasticity is less than 60 cN/dtex, a run-flat traveling durability may not be improved sufficiently.

Still further, the weft 11 preferably has a breaking elongation of 5 to 20% and a breaking strength in a range of 200 to 1000 g. When the breaking elongation is less than 5% or the breaking strength is less than 200 g, the weft 11 is cut unexpectedly before the process that a rubber is topped, thus the shape as a woven screen fabric may not be maintained. On the other hand, when the breaking elongation is more than 20% or the breaking strength is more than 1000 g, the weft 11 is hard to cut during the cutting process, thus the homogeneity in the tire circumferential direction may not be sufficiently improved.

Still further, the weft 11 is preferably composed of cellulosic fibers or vinylon fibers, and is still preferably a spun yarn. Such fibers may be designed such that the fibers satisfy the above-described conditions of the breaking elongation and the breaking strength.

Next, a carcass ply cord including not less than 50% by mass of polyketone fibers (hereinafter, referred to as “PK fiber”) which may be used in the present invention will be described in detail.

Examples of fiber which may be used in the present invention other than PK fiber include nylons, polyesters, rayons, polynosic, lyocell, vinylons and the like.

The above-described cord preferably also has a twist coefficient α represented by the following formula (I):

α=T×√{square root over (0.126×D/ρ)}×10⁻³  (I)

[where T is the number of twist (turn/100 mm), D is total fineness (dtex) of the cord and ρ is a density (g/cm³) of the fiber material which is used for the cord] in a range of 0.25 to 1.25. When the twist coefficient α of the PK fiber cord is less than 0.25, heat shrinkage force may not be secured sufficiently. Whereas, when the twist coefficient α is more than 1.25, the modulus of elasticity may not be secured sufficiently, thus, the reinforcing ability decreases.

As a polyketone which is a raw material of the above-described PK fiber, the one which is substantially composed of repeating units represented by the following general formula (II):

[where A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in each repeating unit] is preferred. Among these, a polyketone which has 97% of 1-oxotrimethylene [—CH₂—CH₂—CO—] by mole of all of the repeating units is preferred, a polyketone which has 99% of 1-oxotrimethylene by mole of all of the repeating units is more preferred, and a polyketone which has 100% of 1-oxotrimethylene by mole of all of the repeating units is most preferred.

In such a polyketone, ketone groups and portions derived from unsaturated compounds may be partially combined among themselves, and the rate of portions in which a portion derived from an unsaturated compound and a ketone group are arranged alternately is preferably 90% by mass, more preferably 97% by mass and most preferably 100% by mass.

In the above-described formula (II), as an unsaturated compound which forms A, ethylene is most preferred, though, unsaturated hydrocarbons other than ethylene, such as propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, acetylene and allene; compounds including unsaturated bonds, such as methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinyl pyrrolidone, diethyl ester of sulnyl phosphonic acid, sodium styrenesulfonate, sodium allylsulfonate, vinyl pyrrolidone, and vinyl chloride; and the like are also preferred.

The degree of polymerization of the above-described polyketone is preferably such that the intrinsic viscosity [η] represented by the following formula (III):

$\begin{matrix} {\lbrack\eta\rbrack = {\lim\limits_{c->0}\frac{\left( {T - t} \right)}{\left( {t \cdot c} \right)}}} & ({III}) \end{matrix}$

[in the above-described formula, t and T are respectively a flowing through period of viscosity tube of a hexafluoroisopropanol with not less than 98% purity and a dilution of polyketone dissolved in the hexafluoroisopropanol at a temperature of 25° C., and c is mass (g) of solute in 100 mL of the above-described dilution] is in a range of 1 to 20 dL/g, more preferably 3 to 8 dL/g. When the intrinsic viscosity is less than 1 dL/g, the molecular weight is so small that it is hard to obtain a high strength polyketone fiber cord and troubles in the course of the step such as napping and breaking during spinning, drying and drawing may occur frequently. Whereas, when the intrinsic viscosity is more than 20 dL/g, it takes time and cost to synthesize a polymer and it is hard to dissolve the polymer uniformly, thereby adversely affecting spinnability and physical properties in some cases.

Still further, the PK fiber preferably has a crystal structure which has a crystallinity of 50 to 90% and a degree of crystalline orientation of not less than 95%. When the crystallinity is less than 50%, it is feared not only that sufficient strength of the fiber be not obtained due to insufficiency of the structure formation of the fiber, but also that the shrinkage characteristics and dimensional stability of the fiber during heating be not stable. Therefore, the crystallinity is preferably 50 to 90%, more preferably 60 to 85%.

As a method of producing the above-described polyketone fiber, (1) a method comprising the steps of spinning an undrawn yarn and subjecting to a multi-stage heat drawing in which a final drawing at the multi-stage heat drawing step is carried out at a specified temperature and drawing ratio, and (2) a method comprising the steps of spinning an undrawn yarn, subjecting to heat drawing and then quenching the fiber after heat drawing under a high tension are preferable. By forming the polyketone fiber through the method (1) or (2), desirable filaments suitable for the production of the above-described polyketone fiber cord may be obtained.

A method of spinning the undrawn yarn of the above-described polyketone is not particularly restricted, but conventionally known methods may be adopted. Specifically, mention may be made of a wet spinning method using an organic solvent such as hexafluoroisopropanol or m-cresol as described in Japanese Unexamined Patent Application Publication No. H02-112413, Japanese Unexamined Patent Application Publication No. H04-228613 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. H04-505344, and a wet spinning method using an aqueous solution such as zinc salt, calcium salt, thiocyanate, or iron salt as described in WO99/18143, WO00/09611, Japanese Unexamined Patent Application Publication No. 2001-164422, Japanese Unexamined Patent Application Publication No. 2004-218189 and Japanese Unexamined Patent Application Publication No. 2004-285221. Among these, the wet spinning method using the aqueous solution of the above-described salts is preferred.

For example, in the wet spinning method using the organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol, m-cresol or the like at a concentration of 0.25 to 20% by mass and extruded through a spinning nozzle to form a fiber, and then, the solvent is removed in a non-solvent bath such as toluene, ethanol, isopropanol, n-hexane, isooctane, acetone, or methyl ethyl ketone bath, whereby the polyketone undrawn fiber may be obtained after washing.

On the other hand, in the wet spinning method using the aqueous solution, the polyketone polymer is dissolved in an aqueous solution such as zinc salt, calcium salt, thiocyanate, or iron salt at a concentration of 2 to 30% by mass and extruded from a spinning nozzle into a coagulation bath at 50 to 130° C. to conduct gel spinning and then desalted and dried to obtain the undrawn polyketone yarn. In the aqueous solution dissolving the polyketone polymer, it is preferable to use a mixture of a zinc halide and a halide of an alkali metal or an alkaline earth metal. In the coagulation bath, water, an aqueous solution of a metal salt, or an organic solvent such as acetone, or methanol may be used.

As the method of drawing the obtained undrawn yarn, a heat drawing method in which the undrawn yarn is drawn by heating to a temperature higher than the glass transition temperature of the undrawn yarn, is preferred. Further, the drawing of the undrawn yarn in the above method (2) may be carried out at one stage, but it is preferable to conduct the multi-stage drawing. The heat drawing method is not particularly restricted, and may adopt a method of running the yarn on, for example, a heat roll or a heat plate, and the like. In this case, the heat drawing temperature is preferably in a range of 110° C. to (the melting point of a polyketone), and the total drawing ratio is preferably not less than 10 times.

When the formation of the polyketone fiber is carried out through the method (1), the temperature at the final drawing step of the above-described multi-stage heat drawing is preferred to be in a range of 110° C. to (drawing temperature at drawing step just before the final drawing step −3° C.), and the drawing ratio at the final drawing step of the multi-stage heat drawing is preferred to be in a range of 1.01 to 1.5 times. On the other hand, when the formation of the polyketone fiber is carried out through the method (2), the tension applied to the fiber after the heat drawing is preferred to be in a range of 0.5 to 4 cN/dtex, and the cooling rate in the quenching is preferred to be not less than 30° C./second, and the cooling-end temperature in the quenching is preferred to be not higher than 50° C. The quenching method of the heat-drawn polyketone fiber is not particularly restricted, and may adopt conventionally known methods. Specifically, the cooling method using the roll is preferred. Further, the thus obtained polyketone fiber has a large retention in the elastic strain, so that it is preferred that the fiber is usually subjected to a relaxation heat treatment so as to make the length of the fiber shorter than the length of the fiber after the heat drawing. In this case, the temperature of the relaxation heat treatment is preferred to be in a range of 50 to 100° C., and the relaxation ratio is preferred to be in a range of 0.980 to 0.999 times.

In order to best utilize the high heat shrinkage characteristics of the PK fiber cord, it is preferred that the treatment temperature during processing and a temperature of the molded article in use are near the temperature which indicates heat shrinkage stress (maximum heat shrinkage temperature). Specifically, because the processing temperature such as the RFL treatment temperature in the adhesive processing which is performed as required or a vulcanizing temperature is 100 to 250° C., and the temperature of the tire material heated by a repetitive usage or a high-speed rotation reaches 100 to 200° C., the maximum heat shrinkage temperature is preferably in a range of 100 to 250° C., more preferably in a range of 150 to 240° C.

The polyketone fiber of the present invention may be suitably produced by melt spinning of polyketone. Specifically, the melt spinning method described in Japanese Patent Publication No. 2763779 may be adopted. That is, a melt polyketone fiber composed of an alternate-type copolymer of olefin unsaturated hydrocarbon and carbon monoxide (copolymer in which a CO unit and an olefin-derived unit are arranged alternately in the macromolecule) may be obtained as the one with desired characteristics having an excellent combination balance of tensile strength, bending modulus and adhesiveness to rubber, by melt spinning an alternate copolymer of carbon monoxide and an olefin unsaturated hydrocarbon having an average molecular weight of not less than 2000 at a temperature of not lower than (T+20) K, then drawing the resultant at a temperature of not higher than (T−10)K (where T is the crystal melting point of the above-described polymer). In this case, the drawing ratio of the drawing is preferably at least 3:1, more preferably at least 7:1, most preferably 15:1. A preferable drawing temperature is lower than the crystal melting point of the polymer by at least 40 K, and a preferable melt spinning temperature is higher than the crystal melting point of the polymer by at least 40 K.

Alternatively, since it is known that melt spinnability is provided when silicon atom is introduced in the molecular chain as described in Japanese Unexamined Patent Application Publication No. 2005-105470, melt spinning may be conducted by using a polyketone produced by the method described in the same publication. That is, a desired polyketone fiber may be obtained by melting a polyketone obtained by reacting ethylene unsaturated compound and carbon monoxide as well as silicone compound as a third ingredient to extrude from a spinning nozzle, and being drawn while being wound temporarily or not being wound. The obtained polyketone fiber has a tensile strength of not less than 5 cN/detex.

As mentioned above, in order to best utilize the high heat shrinkage characteristics of the PK fiber cord, it is preferred that the treatment temperature during processing and a temperature of the molded article in use are near the temperature which indicates heat shrinkage stress (maximum heat shrinkage temperature), and the maximum heat shrinkage temperature is preferably in a range of 100 to 250° C., more preferably in a range of 150 to 240° C.

The coating rubber which covers the carcass ply cord of the present invention may have a variety of shapes. Representative examples of the shapes include a coating and a sheet. As a coating rubber, known rubber compositions may be suitably adopted and should not be particularly restricted.

The run-flat tire of the present invention may be manufactured by a conventional method by applying the above-mentioned carcass ply as the radial carcass 4. As for the pneumatic tire of the present invention, normal air or an air in which the partial pressure of the oxygen is varied, or an inert gas such as nitrogen may be used as a gas which is filled in the tire.

EXAMPLES

In the following, the present invention will be described by way of Examples thereof.

Preparation Example 1 of PK Fiber: Wet Spinning

A polyketone polymer having an intrinsic viscosity of 5.3 in which ethylene prepared by a conventional method and carbon monoxide were perfectly alternately copolymerized were added to an aqueous solution containing 65% by mass of zinc chloride/10% by mass of sodium chloride, and was stirred to be dissolved at a temperature of 80° C. for 2 hours, whereby a dope which had a polymer content of 8% by mass was obtained.

The obtained dope was heated to 80° C., and passed through a 20 μm sintered filter. The resultant dope was extruded from a spinning nozzle having 50 holes with 0.10 mm φ in diameter heated at 80° C. through a 10 mm air gap into 18° C. water containing 5% by mass of zinc chloride at a discharge rate of 2.5 cc/min. The extrudate was drawn at 3.2 m/min to produce a coagulated filament.

Subsequently, the coagulated filament was washed in 2% by mass aqueous sulfuric acid solution at 25° C. and then in water at 30° C., and was wound as a coagulated yarn at 3.2 m/min.

The coagulated yarn was impregnated with IRGANOX 1098 (manufactured by Ciba Specialty Chemicals K.K.) and IRGANOX 1076 (manufactured by Ciba Specialty Chemicals K.K.) at 0.05% by mass (with respect to polyketone polymer) each. The coagulated yarn was dried at least at 240° C. and was treated with a finishing agent to produce undrawn yarn. The heat shrinkage rate may be adjusted by suitably controlling the drying temperature.

The finishing agent had the following composition:

lauryl oleate/bisoxyethyl bisphenol A/polyether (propylene oxide/ethylene oxide=35/65: molecular weight 20000)/10-mole polyethylene oxide added oleyl ether/10-mole polyethylene oxide added castor oil ether/sodium stearylsulfonate/sodium dioctylphosphate=30/30/10/5/23/1/1 (% by mass).

The obtained undrawn yarn was drawn by five steps: 240° C. (1st), 258° C. (2nd), 268° C. (3rd), 272° C. (4th), and 200° C. at a drawing ratio of 1.08 (drawing tension: 1.8 cN/dtex) (5th), and was wound by a winder. The total drawing ratio of the five-step drawn yarn with respect to the undrawn yarn was 17.1. This fiber original yarn had excellent physical properties: a tensile strength of 15.6 cN/dtex, an elongation of 4.2%, and a modulus of elasticity of 347 cN/dtex. The fiber yarn had a heat shrinkage rate of 1.9% in 150° C.×30 min dry heat treatment. The PK fiber thus obtained was used as a cord in the following conditions.

Preparation Example 2 of PK Fiber: Melt Spinning

Fiber brand of alternate copolymer of carbon monoxide, ethylene and 8% by mole of propylene ethylene (PE) based on ethylene was subjected to a melt spinning. The copolymer had a molecular weight of 10,000 to 25,000 and a crystal melting point of 220° C. The melt spinning was conducted at a drawing ratio of 6:1. The drawing temperature of the alternate copolymer was set at 207° C. and the melt spinning temperature of the alternate copolymer was set at 280° C.

Examples 1 to 22, Comparative Examples 1 to 4 and Conventional Example

A cord/rubber complex was prepared by arranging fiber cords having a material, a thickness, a spinning method used, a heat shrinkage stress, a dry heat shrinkage rate, an end count of the polyketone fiber cords at the bead portion, a cord diameter D1 and a single yarn fineness as described in Tables 1 to 3 in parallel, covering with a coating rubber, cutting wefts, and the like. The cord/rubber complex was employed as a carcass ply, and a side reinforcing type run-flat tire having the structure shown in FIG. 1 and having a size of 215/45ZR17 was test-manufactured. A vertical spring and run-flat durability of the obtained tire were evaluated by the following method and the result shown in Table 3 was obtained.

(1) Vertical Spring

A load-deformation curve of the test tire inflated to an inner pressure of 230 kPa was measured, and a gradient of the tangent at a given load on the obtained load-deformation curve was defined as a vertical spring constant with respect to the load. The vertical spring constant of the test tire was indicated as an index by taking the value of the vertical spring constant of the conventional tire of Conventional Example as 100. The larger the value of the index is, the larger the value of the vertical spring constant.

(2) Run-Flat Durability

A drum test was conducted under a condition having a load of 4.17 kN, a velocity of 89 km/h and a temperature of 38° C. without inflating the test tire to determine the travel distance until resulting in a failure of the tire. The travel distance was indicated as an index by taking the travel distance of the tire of Conventional Example until resulting in a failure of the tire as 100. The larger the value of the index is, the longer the travel distance until resulting in a failure of the tire is. The larger index means that the tire excels in run-flat durability.

(3) Tire Uniformity

The RFV (Radial Force Variation) and LFV (Lateral Force Variation) of the test tire inflated to an inner pressure of 230 kPa were determined and each was indicated as an index by taking the value of the vertical spring constant of the tire of Conventional Example as 100. The smaller the index is, the more preferable the uniformity of the tire.

TABLE 1 carcass cord end heat count single shrinkage heat (cord cord yarn material · spinning force shrinkage number/ diameter fineness thickness method (cN/dtex) rate (%) 100 mm) D1 (mm) (dtex) Conventional Rayon wet spinning 0.06 1.2 80 0.84 2.2 Example 1840dtex/3 Comparative Rayon wet spinning 0.06 1.2 80 0.84 2.2 Example 1 1840dtex/3 Comparative Rayon wet spinning 0.06 1.2 85 0.84 2.2 Example 2 1670dtex/3 Comparative PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 3 Example 1 PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 2 PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 3 PK 1670dtex/2 wet spinning 0.85 2.3 95 0.73 1.6 Example 4 PK 1670dtex/2 wet spinning 0.65 1.8 95 0.73 1.6 Example 5 PK 1670dtex/2 wet spinning 0.42 1.6 95 0.66 1.6 Example 6 PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 7 PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 8 PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Comparative PK 1670dtex/2 wet spinning 0.92 2.7 95 0.73 1.6 Example 4 Example 9 PK 1670dtex/2 wet spinning 0.92 2.7 88 0.73 1.6 Example 10 PK 2200dtex/2 wet spinning 0.94 2.9 72 0.84 1.6 Example 11 PK 1100dtex/2 wet spinning 0.91 2.5 104 0.59 1.6 Example 12 PK 1670dtex/2 wet spinning 0.85 2.3 88 0.66 1.6 Example 13 PK 2200dtex/2 melt spinning 0.6 3.5 95 0.85 5.0 Example 14 PK 1100dtex/2 melt spinning 0.4 5.5 95 0.59 4.0 Example 15 PK 1670dtex/2 melt spinning 0.38 3.2 95 0.69 4.5 Example 16 PK 1670dtex/2 melt spinning 0.45 5.1 95 0.73 5.0 Example 17 PK 1670dtex/2 melt spinning 0.5 6.0 95 0.69 5.0 Example 18 PK 1670dtex/2 melt spinning 0.5 6.0 95 0.69 2.0 Example 19 PK 1670dtex/2 melt spinning 0.5 3.0 95 0.66 4.5 Example 20 PK 1670dtex/2 melt spinning 0.45 3.3 95 0.66 12 Example 21 PK 1670dtex/2 melt spinning 0.15 3.1 95 0.69 1.2 Example 22 PK 1670dtex/2 melt spinning 0.72 3.2 95 0.69 16

TABLE 2 weft end count cut pitch cut pitch (cord breaking breaking at center at bead number/ Diameter cut/ elongation strength portion portion material · thickness 100 mm) D2 (mm) no cut (%) (g) (mm) (mm) Conventional Polynosic 300dtex/1 8 0.18 no cut 12 500 — — Example Comparative Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 1 Comparative Polynosic 300dtex/1 8 0.18 cut 12 500 17.6 12.4 Example 2 Comparative Lyocell 300dtex/1 8 0.18 no cut 11 600 — — Example 3 Example 1 Lyocell 300dtex/1 8 0.18 cut 11 600 9.0 6.0 Example 2 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 3 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 4 Lyocell 300dtex/1 8 0.18 cut 11 600 9.0 6.0 Example 5 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 6 Cotton 420dtex/1 8 0.15 cut 9 550 9.0 6.0 Example 7 Lyocell 300dtex/1 8 0.18 cut 11 600 18 12 Example 8 Polynosic 300dtex/1 8 0.18 cut 12 500 24 16 Comparative high elongation Nylon 8 0.15 cut 80 700 not uniformly cut Example 4 300dtex/1 Example 9 Polynosic 300dtex/1 8 0.18 cut 12 500 17.3 12 Example 10 Polynsic 400dtex/1 5 0.21 cut 11 620 57.7 41.2 Example 11 Polynosic 200dtex/1 16 0.14 cut 12 390 11.5 8.2 Example 12 Polynosic 300dtex/1 8 0.18 cut 12 500 18.4 14 Example 13 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 14 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 15 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 16 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 17 Polynosic 300dtex/1 8 0.18 cut 12 500 9.0 6.0 Example 18 Cotton 420dtex/1 8 0.15 cut 9 550 9.0 6.0 Example 19 Lyocell 300dtex/1 8 0.18 cut 11 600 9.0 6.0 Example 20 Lyocell 300dtex/1 8 0.18 cut 11 600 9.0 6.0 Example 21 Polynosic 300dtex/1 8 0.18 cut 11 600 9.0 6.0 Example 22 Polynosic 300dtex/1 8 0.18 cut 11 600 9.0 6.0

TABLE 3 tire performance reinforcing vertical stiffness rubber during normal run-flat uniformity thickness travel durability (index) (mm) (index) (index) RFV LFV Conventional 8.5 100 100 100 100 Example Comparative 8.5 100 100 95 98 Example 1 Comparative 8.5 100 100 95 98 Example 2 Comparative 6.5 90 9 104 100 Example 3 Example 1 6.5 90 200 92 97 Example 2 6.5 90 200 92 97 Example 3 6.5 91 180 93 97 Example 4 6.5 92 160 94 98 Example 5 6.5 94 140 95 99 Example 6 6.5 90 200 92 97 Example 7 6.5 90 200 94 98 Example 8 6.5 90 200 96 99 Comparative 6.5 90 9 104 101 Example 4 Example 9 6.5 90 200 92 97 Example 10 6.5 94 240 96 99 Example 11 6.5 86 160 88 92 Example 12 6.5 91 180 93 97 Example 13 6.0 90 170 92 97 Example 14 6.0 90 130 97 97 Example 15 6.0 94 135 98 98 Example 16 6.0 92 145 95 97 Example 17 6.0 91 150 90 96 Example 18 6.0 90 150 90 97 Example 19 6.0 90 150 93 97 Example 20 6.0 90 145 95 97 Example 21 6.0 90 145 94 97 Example 22 6.0 90 145 93 98

The above-described Table 1 shows that the tire having the configuration of the present invention excels in the uniformity. Further, the above-described Table 1 shows that, by applying a pick breaker treatment, the uniformity of the tire employing the melt spinned PK fiber may be more improved. 

1. A run-flat tire comprising a left-and-right pair of bead portions, a carcass ply extending from a crown portion to the pair of bead portions by way of each of the side portions, and a side reinforcing rubber layer having a crescent-shaped meridional cross section which layer extends all over or almost all over the both side portions along the inside of the carcass ply, wherein the carcass ply cord contains at least 50% by mass of polyketone fibers, has a heat shrinkage force of 0.1 to 1.8 cN/dtex as a cord subjected to a dipping process, and the heat shrinkage rate of the polyketone fiber in a dry heat treatment at a temperature of 150° C. for 30 minutes is in a range of 0.3 to 6.5%; and wherein the carcass ply includes a weft which crosses the cords arranged approximately along the radial directions, and the weft is cut at a plurality of points at regular intervals along the tire circumferential direction.
 2. The run-flat tire according to claim 1, wherein the end count of the polyketone fiber cords at the bead portion of the carcass ply is in a range of 70 to 120 cords/100 mm.
 3. The run-flat tire according to claim 1, wherein the end count of the weft is in a range of 3 to 20 cords/100 mm.
 4. The run-flat tire according to claim 1, wherein the cord diameter D1 of the carcass ply cord is in a range of 0.45 to 0.95 mm.
 5. The run-flat tire according to claim 1, wherein the diameter D2 of the weft is in a range of 0.1 to 0.3 mm.
 6. The run-flat tire according to claim 1, wherein the cut pitch A of the weft is 5.5 to 60 times the cord diameter D1.
 7. The run-flat tire according to claim 1, wherein as the polyketone fiber included in the fiber cord which forms the carcass ply, the tensile strength of the original fiber is not less than 10 cN/dtex and the modulus of elasticity of the fiber is not less than 60 cN/dtex.
 8. The run-flat tire according to claim 1, wherein the breaking elongation of the weft is 5 to 20% and the breaking strength of the weft is in a range of 200 to 1000 g.
 9. The run-flat tire according to claim 1, wherein the weft is composed of cellulosic fiber or vinylon fiber.
 10. The run-flat tire according to claim 1, wherein the weft is spun yarn. 